Conjugated polymers have received considerable attention as the active materials in fluorescence-based chemical sensors because of their high sensitivity to a variety of solution- and vapor-phase analytes. The response characteristics of a thin-film polymer fluorescence sensor depend strongly on a number of factors including the permeability of the analyte in the polymer, and the strength of the chemical (or physical) interaction between the analyte and the photoactive polymer, where permeability (P) is the product solubility (S) and diffusivity (D) of an analyte in a polymer, i.e., P=S*D. Recently, it has been demonstrated that by using a sterically demanding pentiptycene moiety it is possible to increase the permeability of a highly fluorescent poly(phenyleneethynylene) film thereby increasing the response of the material to vapor-phase analytes. The bulky pentiptycene moiety is believed to create molecular-scale channels which provide pathways for the analyte molecules to diffuse into the polymer and readily interact with the electron-rich π-conjugated system. The resulting increase in permeability of the pentiptycene-substituted poly(phenyleneethynylene) film can allow the analyte to quench the polymer's fluorescence more rapidly and efficiently compared to similar polymers that lack the sterically-demanding pentiptycene group. Others have demonstrated that doping a surfactant into a film of a fluorescent conjugated polyelectrolyte considerably improves the film's response to neutral analyte molecules. The surfactant is believed to improve the fluorescence response by increasing the solubility (sorption) of the neutral analyte in the film.